In the past, a flexible disk clamping device for use in a flexible disk driving apparatus and as shown in FIGS. 1 and 2 has been available.
In the clamping device shown in FIG. 1, a collet 1 is pivotally mounted on a collet shaft 3, said collet 1 being provided with a suitable number of slits 2 in a cover-like body having a flange and being formed in the form of a petal. The collet shaft 3 is moved down to clamp the inner peripheral edge of a disk 5 between the peripheral edge 4a of a spindle hub 4 and a flange on the collet 1.
However, the prior art clamping device shown in FIG. 1 is designed so that the outside diameter of the collet 1 is larger than the inside diameter of the spindle hub 4, and therefore, the device suffers from such disadvantages as that when clamping, the collet may not be forced into the hub completely and may run on to the hub, thus damaging the center of the flexible disk 5 and impairing the normal rotation thereof.
The clamping device shown in FIG. 2 is designed so that a petal-like collet 6, similar to the collet shown in FIG. 1, is turned over and pivotally mounted on a collet shaft 7 so that it is axially slidable. A wedge board 9 is mounted on a bearing 8 on the collet shaft 7, and a biasing spring 10 is provided between the wedge board 9 and the collet 6.
Also in the clamping device, the collet shaft 7 is moved down, the outside diameter of the collet is increased by the wedge board 9, and the flexible disk 5 is clamped between the peripheral edge 4a of the spindle hub 4 and the flange 6a of the collet 6 in a manner similar to that shown in FIG. 1. This device also has disadvantages, such that the outside diameter of the collet 6 cannot reach a desired size if there is an error in manufacture, a temperature change, or a change of size after passage of time. Thus a clearance may be formed between the center hole of the flexible disk 5 and the collet 6, and the center of the flexible disk shifts away from the center rotation.
When the center of the flexible disk is offset relative to the center of rotation as described above, a so-called head deviation occurs during write-in and read-out, significantly influencing the performance of a read/write device using the flexible disk. The greater the write-in density, the greater the bad influence due to the offset.